Blood Pressure
• An Individuals blood pressure is a standard clinical
measurement
• Is considered a good indicator of the status of the
cardiovascular system.
• Blood pressure values in the various chambers of the heart
and in the peripheral vascular system help the physician
determine the functional integrity of the cardio vascular
system.
Blood Pressure inside the heart chambers
Major Arteries & Veins of the Body
Cardiovascular system-typical values
Blood Pressure Measurement
• Direct (invasive)
1. Extravascular Method
• The vascular pressure is coupled to an external sensor
element via a liquid filled catheter.
[Catheter – is a long tube introduced into the heart or a major vessel by way of a
superficial vein or artery.]
2. Intravascular
• A sensor is placed into the tip of a catheter that is placed in
the vascular system.
• Indirect (non invasive)
• Sphygmomanometer
Consists of an inflatable pressure cuff and a manometer to
measure the pressure in the cuff.
Direct Measurement
(Extravascular)
Disposable blood-pressure sensor with integral flush device
Direct Measurement
Extra Vascular
• The extra vascular sensor system is made up of a
catheter.
• The catheter is connected to a three way stopcock
and then to a pressure sensor
• It is filled with a saline-heparin solution.
• It must be flushed with solution every few minutes
to prevent blood clotting at the tip.
Direct Measurement
Extra Vascular contd…
• Physician inserts the catheter
• Either by means of a surgical cut-down, which exposes the artery
or vein.
• or by means of percutaneous insertion which involves the use of a
special needle or guide-wire technique.
• Blood pressure is transmitted via the catheter column to
the sensor and finally to the diaphragm which is deflected.
• The displacement of the diaphragm is sensed electronically.
Direct Measurement
Extra Vascular contd…
• Disadvantages
• The frequency response of the catheter-sensor system
is limited by the hydraulic properties of the system.
• Creates time delay in detection of pressures when a
pressure pulse is transmitted.
Direct Measurement
Intravascular
• The sensor is placed at the tip of the catheter.
• Enables the physician to obtain a high frequency response
in detection of pressures at the tip of the catheter.
• Types of sensors
1. Strain-gage systems
• bonded onto a flexible diaphragm at the catheter tip.
2. Fibre-optic device
• Measures the displacement of the diaphragm optically by
varying reflection of light from the back of the deflecting
diaphragm.
Bonded Strain Gage pressure transducer
•
Consists of strain-sensitive gages which are firmly
bonded with an adhesive to the membrane or
diaphragm whose movement is to be recorded.
•
Made by taking a length of a very thin wire or foil
which is formed into a grid pattern and bonded
to a backing material.
•
Is then attached to the diaphragm.
•
Deflection of the diaphragm causes
corresponding strain in the wire gage.
•
Causes a corresponding change in the resistance
which is proportional to the pressure.
Fiber optic type pressure transducer
• Measures the displacement of the diaphragm
optically by the varying reflection of light from the
back of the deflecting diaphragm.
• Inherently safer electrically
Blood Pressure Waveforms
Harmonic Analysis of Blood Pressure
Waveforms
Harmonic Analysis of Blood Pressure
Waveforms
• Using Fourier Analysis techniques
quantification of pressure and flow.
in
the
• Blood pressure pulse can be divided into its
fundamental component (of the same frequency as
the blood pressure wave) and its significant
harmonics.
• Analysis of the frequency components of the pulse
yield more information on arterial properties.
Electrical Model of Catheter-Sensor system
Testing technique for measuring the transient response of
the catheter-sensor system
Transient response of the catheter-sensor system
Pressure-waveform distortion
Distortion during the recording of arterial pressure
Venous pressure
• For determining the function of
• Capillary bed
• Right side of the heart
• The central venous pressure is measured in the central vein or in
the right atrium.
• It fluctuates above and below atmospheric pressure as the
subject breathes.
• The reference level for venous pressure is at the right atrium.
• Central venous pressure is an important indicator of myocardial
performance
Central venous pressure
• Monitored for assessing proper therapy for
• heart dysfunction
• Shock
• Hypovolemic
circulating blood)
(Of or relating to a decrease in the volume of
or hypervolemic States
• Circulatory failure
• Physicians usually measure steady state or
mean venous pressure by making a
percutaneous venous puncture with a large
bore needle, inserting a catheter through the
needle .
• Needle is then removed.
Central venous pressure
• Continuous dynamic measurements is
made by connecting a high sensitive
pressure sensor to the venous catheter.
• Normal venous pressure values range
widely from 0 to 1.2 kPa with a mean
pressure of 0.5 kPa(0 – 12cm H2O).
Heart Sounds
• Heart sounds are vibrations or sounds due to the
acceleration or deceleration of blood.
• Murmurs are vibrations or sounds due to blood
turbulence.
• The technique of listening to sounds produced by
the organs and vessels of the body is called
auscultation.
Heart Sounds …
Heart Sounds …
Heart Sounds …
•
With each heartbeat, the normal heart produces two distinct sounds that are
audible in the stethoscope – often described as “lub-dub”
•
The “lub” is caused by the closure of atrioventricular valves and is called the first
heart sound
• occurs approximately at the time of QRS complex of the ECG and just before
ventricular systole.
•
The “dub” part of the heart sounds is called the second heart sound and is caused
by the closing of the semilunar valves
• Which closes at the end of the systole, just before the atrioventricular valve
opens.
•
•
Occurs at the time of the end of the T wave of the ECG
The third heart sound attributed to the sudden termination of the rapid filling
phase of the ventricles from the atria and the associated vibration of the
ventricular muscle walls., which are relaxed.
• Fourth or atrial heart sound – not audible ,
can be recorded by phonocardiogram, due to
atria contract
Auscultation Techniques
• There are optimal recording sites for the various heart sounds.
Auscultation Techniques…
• Heart sounds and murmurs have extremely small
amplitudes with frequencies from 0.1 to 2000 Hz.
• Thus the recording device must be carefully
selected for wide band frequency response
characteristics.
• Specially designed acoustically quiet environment is
needed for noise free recording of heart sounds.
Stethoscope
• Mechanical stethoscopes amplifies sound because of Standing wave
phenomenon.
• Firm application of the chest piece makes the diaphragm taut
with pressure thereby causing an attenuation of low frequencies.
• Loose-fitting earpiece cause leakage which reduces the coupling
between the chest wall and the ear.
• Electronics stethoscopes has selectable frequency response
characteristics ranging from “ideal” flat-response to selectable bandpass response.
Stethoscope Frequency response
Phonocardiogram
• A Phonocardiogram is a recording of the heart sounds and
murmurs.
• Eliminates subjective interpretation of the heart sounds
• Enables evaluation of the heart sounds and murmurs with
respect to the electric and mechanical events in the cardiac
cycle.
• Evaluation of the result is based on the basis of changes in
the wave shape and various timing parameters.
Phonocardiogram
Frequency spectrum of a typical
Phonocardiogram
Cardiac Catheterization
• The process of introducing a catheter into the heart for
diagnosis.
• Used to asses hemodynamic (circulation of the blood and
the forces involved) function and cardiovascular structure.
• Performed during most of the heart surgeries.
• Performed in specialized laboratories outfitted with x-ray
equipment for visualizing heart structures and the position
of various pressure catheters.
Cardiac Catheterization …
• A radiopaque die is injected into the ventricles
or aorta through the catheter for assessing
the ventricular or aortic function
• Pressures in all four chambers of the heart
and in the great vessels can be measured by
positioning the catheters in such a way to
recognize the characteristics pressure
waveforms.
Cardiac Catheterization …
Angiography
• Angiographic visualization is an essential tool used
to evaluate cardiac structure.
• Specially designed catheters and power injectors
are used in order that a bolus of contrast material
can be delivered rapidly into the appropriate vessel
or heart chamber.
• During catheterization cardiac catheterization
frequently occur. Clinics must have a functional
defbrillaltor
Cardiac Catheterization & Angiogram
Angiogram
Angeography Types
•
•
•
•
Left & Right ventricle – ventriculography
Coronary arteries – coronory angeography
Pulmonary artery – pulmonary angeography
Aorta- aortography
Angioplasty
• Surgical procedure to repair a
damaged blood vessel or unblock a
coronary artery.
• PTCA – Percuntaneous Transluenal
Coronary Angeoplasty
Indirect Blood Pressure Measurement - Sphygmomanometer
Indirect Blood Pressure Measurement - Sphygmomanometer
Indirect Blood Pressure Measurement - Sphygmomanometer
Indirect Blood Pressure Measurement - Sphygmomanometer
• The pressure cuff on the upper arm is first
inflated to a pressure well above the systolic
pressure.
• At this point no sound can be heard through
the stethoscope, which is placed over the
brachial artery, for that artery has been
collapsed by the pressure of the cuff.
• The pressure in the cuff is then gradually
reduced.
Sphygmomanometery…
• When the systolic peaks are higher than the
occlusive pressure, the blood spurts under
that cuff and causes a palpable pulse in the
wrist (Riva-Rocci Method)
• Audible sounds (Korotkoff (named after Dr.
Nikolai Korotkoff) sounds) generated by the
flow of blood and vibrations of the vessel
under the cuff are heard through the
stethoscope.
Sphygmomanometery …
• The pressure of the cuff that is indicated on
the manometer when the first Korotkoff
sound is heard is recorded as the systolic
blood pressure.
• As the pressure in the cuff is continues to
drop, the Korotkoff sounds continue until the
cuff pressure is no longer sufficient to occlude
the vessel during any part of the cycle. Below
this pressure the Korotkoff sounds disappear,
marking the value of the diastolic pressure.
Sphygmomanometery …
• Auscultatory (based on the Korotkoff sounds)
technique is simpler and requires a minimum
of equipment.
• Cannot be used in noisy environments.
• Palpation (based on pulse on the blood
vessel) technique doesn’t require a noise free
environment.
• Normal respiration and vasomotor waves
modulate the normal blood-pressure levels.
Automated Indirect Blood Pressure measurement
techniques
• Involves an automatic sphygmomanometer
that inflates and deflates an occlusive cuff at a
predetermined rate.
• A sensitive detector is used to measure the
distal pulse or cuff pressure.
Automated Auscultatory device
• Microphone replaces the stethoscope for
sensing the Korotkoff sounds.
• The process begins with a rapid (20-30mm
Hg/s) inflation of the occlusive cuff to a preset
pressure about 30mm Hg higher that the
suspected systolic pressure.
• The flow of blood beneath the cuff is stopped
by the collapse of the vessel.
Automated Auscultatory device
• Cuff pressure is then reduced slowly (2-3 mm
Hg/s).
• The first Korotkoff sound is detected by the
microphone, at which time the level of the
cuff pressure is stored.
Automated Auscultatory device
• The muffling and silent period of the Korotkoff
sound is detected, and the value of the
diastolic pressure is also stored.
• After a few minutes the instrument displays
the systolic and diastolic pressure and recycles
the operation
Ultrasonic Based Blood Pressure Measurement
• Employs a transcutaneous Doppler sensor
that detects the motion of the blood-vessel
walls in the various states of occlusion.
• The Doppler ultrasonic transducer is focused
on the vessel wall and the blood.
• The reflected signal (shifted in frequency) is
detected by the receiving crystal and
decoded.
Ultrasonic Based Blood Pressure Measurement…
Ultrasonic Based Blood Pressure Measurement…
• The difference in frequency, in the range of 40
to 500 Hz, between the transmitted and
received signals is proportional to the velocity
of the wall motion and the blood velocity.
Ultrasonic Based Blood Pressure Measurement…
• As the applied pressure is further increased,
the time between the opening and closing
decreases until they coincide. The reading at
this point is the systolic pressure.
• When the pressure is cuff is reduced, the time
between the opening and closing increases
until the closing signal from one pulse
coincides with opening signal from the next.
The reading at this point is the diastolic
pressure.
Ultrasonic Based Blood Pressure Measurement…
• Advantages:
• Doesn’t require a noise free environment.
• Disadvantage:
• Movement of the subject‘s body cause
changes in ultrasonic path between the
sensor and the blood vessel.
Electromagnetic Blood Flow Meters
• Measures instantaneous pulsatile flow of
blood
• Works based on the
electromagnetic induction
principle
of
• The voltage induced in a conductor moving in a
magnetic field is proportional to the velocity of the
conductor
• The conductive blood is the moving conductor
Principle of Electromagnetic Blood Flow Meters
Principle of Electromagnetic Blood flow Measurement
Principle of Electromagnetic Blood Flow Meters
• A permanent magnet or electromagnet
positioned around the blood vessel generates
a magnetic field perpendicular to the
direction of the flow of the blood.
• Voltage induced in the moving blood column
is measured with stationary electrodes
located on opposite sides of the blood vessel
and perpendicular to the direction of the
magnetic field.
Principle of Electromagnetic Blood Flow Meters
• The Induced emf
• Where
• B = magnetic flux density, T
• L = length between electrodes, m
• u = instantaneous velocity of blood, m/s
Principle of Electromagnetic Blood Flow Meters
• This method requires that the blood vessel be
exposed so that the flow head or the
measuring probe can be put across it.
Design of Flow Transducers
• The electromagnetic flow-transducer is a tube of
non-magnetic material to ensure that the magnetic
flux does not bypass the flowing liquid and go into
the walls of the tube.
• The tube is made of a conducting material and
generally has an insulating lining to prevent short
circuiting of induced emf.
• The induced emf is picked up by point electrodes
made from stainless steel or platinum.
Design of Flow Transducers
• The flow head contains a slot through which the
intact blood vessel can be inserted to make a snug
fit.
• Several probes of different sizes must therefore
accompany the flowmeter to match the full range
of sizes of the blood vessels which have various
diameters.
• Flow heads having as small as 1mm are available.
Types of Electromagnetic Blood Flow Meters
• DC Flow meters
• Use DC Magnetic field.
• Cause electrode polarization and amplifier drift.
• o/p same as ECG
• Poor SNR
• AC Flow meters
• Electromagnets are driven by alternating
currents.
• The transducer acts like a Transformer and
induces error voltages that often exceed the
signal levels by several orders of magnitude.
Electromagnetic AC flow meters
• Error recovery is achieved by using several different
waveforms for magnet current
• Sine, Square, Trapezoidal.
• Suitable balancing circuits are used to balance out
the error voltage.
Sine wave Flowmeters
• The transformer induced voltage is 90˚ out of
phase and is eliminated by
• Injecting a voltage of equal strength and
opposite phase into the signal.
• Using a gated amplifier.
• Permit the amplification of the signal
only during the flow induced voltages are
maximum and the transformer induced
voltages are minimum.
Square wave Flowmeters
• The transformer induced voltage is only a
spike.
• Separation is easier as the amplifier can be
gated only for a very short period.
• Blanking is required only when the current in
the magnet is reversing its direction and the
amplifier works during the flat portion of the
square wave.
Magnetic Flowmeter Block Diagram
Magnetic Flowmeter Block Diagram
• The oscillator, which drives the magnet
provides a control signal for the gate, operates
at a frequency of between 60 and 400 Hz.
• The frequency response is high enough to
allow the recording of the flow pulses.
• The mean or average flow can be derived by
use of a low-pass filter.
Ultrasonic Blood Flow Meters
• A beam of ultrasonic energy is used to
measure the velocity of flowing blood.
. Lead zirconate titanate is a crystal that has the
highest conversion efficiency.
• Two types:
• Transit time flow meters
• Doppler type.
Transit-Time Ultrasonic Flow Meters
Ultrasonic
Transducer
Ultrasonic
Transducer
Transit-Time Ultrasonic Flow Meters
• Where
• t
• D
• c
• u
- transit time
- Distance between the transducers
- Sound velocity
- blood flow velocity
Transit-Time Ultrasonic Flow Meters
• The pulsed beam is directed through a blood
vessel at a shallow angle and its transit time is
measured.
• The transit time is shortened when the blood
flows in the same direction as the transmitted
energy
• The transit time is lengthened otherwise.
Doppler Type Ultrasonic Flow Meters
Doppler type Ultrasonic Flow Meters
• Based on the Doppler principle
• A transducer sends an ultrasonic beam with a
frequency F into the flowing blood.
• A small part of the transmitted energy is
scattered back and is received by a second
transducer arranged opposite the first one.
• The reflected signal has a different frequency
F + FD or F – FD due to Doppler effect.
Doppler Frequency equation
• Where
• fd = Doppler frequency shift
• f0 = source frequency
• u = target velocity
• c = velocity of sound
Doppler type Ultrasonic Flow Meters…
• The Doppler component FD is directly
proportional to the velocity of the flowing
blood.
• A fraction of the transmitted ultrasonic energy
reaches the second transducer directly with
the frequency being unchanged.
Doppler Type Ultrasonic Flow Meters
Doppler type Ultrasonic Flow Meters…
• After amplification of the composite signal,
the Doppler frequency can be obtained at the
output of the detector as the difference
between the direct and the scattered signal
components.
• For normal blood velocities, the Doppler
signal is typically in the low audio frequency
range.
• Indicator Dilution that uses continuous infusion
(Indicator – Oxygen)- samples from artery &
Pulmonary artery
• Indicator Dilution method that uses rapid
injection
• Dye dilution -indocyanine green – cardio greendye injected to pulmonary artery – samples from
artery
• Thermo Dilution – cold saline- injected to RAtemp measured in pulmonary artery
Indicator Dilution Method of Blood Flow Measurement
• An Indicator I is mixed with the blood with a
known injection rate.
• The Concentration C of the indicator is
measured after mixing.
• Then the flow,
Indicator Dilution Method of Blood Flow Measurement
Indicator Dilution Method of Blood Flow Measurement
• When a given quantity of m0 of an indicator is
added to a volume V, the resulting
concentration C of the indicator is given by
• C = m0/V
• When an additional quantity m of indicator is
then added, the incremental increase in
concentration is
• ΔC = m/V
Indicator Dilution Method of Blood Flow Measurement
• When the fluid volume in the measured space
is continuously removed and replaced, then in
order to maintain a fixed change in
concentration, a fixed quantity of indicator
per unit time must be added continuously.
• ΔC = (dm/dt) / (dV/dt)
• Then the Flow,
Fick Technique to measure blood flow from the heart
• Where
• F = Blood flow, liters/min
• dm/dt = consumption of O2, liters/min
• Ca = arterial concentration of O2, liters/min
• Cv = venous concentration of O2, liters/min
Fick Technique to measure blood flow from the heart
Fick Technique to measure blood flow from the heart
• The blood returning to the heart from the
upper half of the body has a different
concentration of O2 from the blood returning
fromthe lower half.
• The O2 concentration measured by the
spirometer
• The arterial-venous concentration difference
is measured by drawing samples through
catheters placed in an artery and in the
pulmonary artery.
• Cv can be measure it in the pulmonary artery
after it has been mixed by the pumping action
of the right ventricle.
• The clinician can measure the concentration
of the oxygenated blood Ca in any artery.
Fick’s Technique - Advantage
• The Fick technique is nontoxic, because the
indicator (O2) is a normal metabolite that is
partially removed as blood passes through the
systemic capillaries.
• The cardiac output must be constant over several
minutes so that the investigator can obtain the
slope of the curve for O2 consumption.
• The presence of the catheter causes a negligible
change in cardiac output.
Indicator Dilution Method that uses
rapid injection
Rapid-injection indicator-dilution
curve
• Bolus is injected at time A
• There is a transportation delay before the
concentration begins rising at time B.
• After the peak is passed, the curve enters an
exponential decay region between C and D, which
would continue decaying along the dotted curve to t1 if
there were no recirculation.
• Recirculation causes a second peak at E before the
indicator becomes thoroughly mixed in the blood at F.
• The dashed curve indicates the rapid recirculation that
occurs when there is a hole between the left and right
sides of the heart.
• An increment of blood of volume dV passes
the sampling site in time dt.
• quantity of indicator dm contained in dV is
the concentration C(t) times incremental
volume.
• Hence dm =C(t) dV . Dividing by dt, we obtain
(dm/dt)= C(t) (dV/dt)
• dm= Fi C(t) dt
• where t1 is the time at which all effects of the
first pass of the bolus have died out (point E).
• The integrated quantity (∫ C(t) dt) ) is equal to
the shaded area in Figure we can obtain it by
counting squares or using a planimeter.
• If the initial concentration of indicator is not
zero—as may be the case when there is
residual indicator left over from previous
injections( C(t) - > ∆ C(t) )
Properties of Indicator
•
•
•
•
•
(1) inert,
(2) harmless,
(3) measurable,
(4) economical,
(5) always intravascular.
DYE DILUTION
• A common method of clinically measuring cardiac
output is to use a
• colored dye, indocyanine green (cardiogreen).
• It meets the necessary requirements for an
indicator
• The dye is available as a liquid that is diluted in
isotonic saline and injected directly through a
catheter, usually into the pulmonary artery.
• About 50% of the dye is excreted by the kidneys
in the first 10 min, so repeat determinations are
possible.
• The plot of the curve for concentration versus
time is obtained from a constant-flow pump,
which draws blood from a catheter placed in
the femoral or brachial artery.
• Blood is drawn through a colorimeter cuvette
which
continuously
measures
the
concentration of dye, using the principle of
absorption photometry.
Thermo Dilution
• Injecting a bolus of cold saline as an indicator.
• A special four-lumen catheter is floated through
the brachial vein into place in the pulmonary
artery.
• 1- A syringe forces a gas through one lumen;
• 2-The cooled saline indicator is injected through
the second lumen into the right atrium.
• 3- The third lumen carries the thermistor wires.
• 4- Used for withdrawing blood samples.
• The gas inflates a small, doughnut-shaped
balloon at the tip.
• The indicator is mixed with blood in the right
ventricle.
• The resulting drop in temperature of the
blood is detected by a thermistor located near
the catheter tip in the pulmonary artery